When the glucose concentration of blood is measured, a method of using a disposable analysis tool is being employed as a simple and easy technique. Analysis tools include, for example, an electrode-type biosensor 9 shown in FIGS. 9 and 10 herein (for example, refer to Japanese Patent Application Laid-Open (JP-A) No. 6-109688). This biosensor 9 has electrodes 91 and 92 provided in a substrate 90 and a fluid path 93 for moving a sample such as blood.
The electrode 91 has a reactive electrode 94 for performing transfer of electrons to/from a certain component of blood. The electrode 92 has a counter electrode 95 for generating an electric potential difference from the reactive electrode 94. The reactive electrode 94 and the counter electrode 95 are exposed in the fluid path 93 and also make contact with the reagent portion 96.
In such a biosensor 9, when a voltage is applied between the reactive electrode 94 and the counter electrode 95 while the fluid path 93 is supplied with the sample, a response electric current can be output in response to the concentration of a certain component within the sample. Therefore, in the biosensor 9, it is possible to measure the glucose concentration by measuring the response electric current using the reactive electrode 94 (the electrode 91) and the counter electrode 95 (the electrode 92).
Here, the electrodes 91 and 92 of the biosensor 9 is formed by screen printing using ink containing conductive components such as carbon or silver, metal sputtering, or burying metal pieces in the substrate 90. Therefore, the electrodes 91 and 92 have little or substantially no thickness, and the area of the reactive electrode 94 substantially affect the sensor sensitivity of the biosensor 9. Meanwhile, the biosensor 9 tends to be made to have a smaller size of the fluid path 93 to reduce the necessary amount of the sample and also reduce the areas of the electrodes 91 and 92 and, further, the areas of the reactive electrode 94 and the counter electrode 95. Therefore, when the size of the fluid path 93 is reduced, since the contact area making contact between the sample and the reactive electrode 94 when the fluid path 93 is supplied with the sample tends to be reduced, the output of the biosensor 9 is also reduced, and the sensor sensitivity may be easily dispersed.
In addition, the reagent portion 96 is formed by, for example, attaching a reagent liquid to cover the reactive electrode 94 and/or the counter electrode 95 and drying the reagent liquid. When the reagent liquid is dried, the circumferential portion of the attaching spot is more rapidly dried in comparison with the center portion of the attaching spot of the reagent liquid. Therefore, the circumference of the attaching spot is crystallized first, and the circumference of the reagent portion 96 has a higher concentration of the reagent in comparison with the center portion. As a result, when the reagent portion 96 is dissolved by the sample, the solubility of the reagent portion 96 is degraded, or unevenness in the reagent concentration is generated, so that the measurement accuracy may be degraded. In order to address this problem, since it is necessary to prepare a drying apparatus capable of appropriately controlling environmental conditions such as humidity or temperature, expensive equipment is demanded, and cumbersome efforts is necessary to drive or maintain the apparatus.
Furthermore, when the electrodes 91 and 92 are formed by burying metal pieces in the substrate 90, it is necessary to increase the thickness of the entire substrate. Therefore, when the biosensor 9 is manufactured, it may be impossible to perform a manufacturing process by extracting materials such as the substrate 90 from a roll. In other words, since it is difficult to perform a roll-to-roll manufacturing process, the manufacturing method is limited, and it is difficult to improve the manufacturing efficiency.